Microwave oscillator circuits provide energy at microwave frequencies for various systems, including communication, radar and navigation systems. In addition to an active amplifier element, a dielectric resonator oscillator includes a resonant circuit having a dielectric resonator made of a ceramic material for determining the frequency of oscillation. The primary characteristics of the resonant circuit are its quality factor Q and the ceramic material's temperature coefficient .tau..sub.f and dielectric constant .epsilon..sub.r.
In general, designers of dielectric resonator oscillators may select various resonant circuits with different Q, .tau..sub.f and .epsilon..sub.r values depending on design requirements. Typical dielectric resonant circuits have high dielectric constants (e.g., between 37 and 100) and high quality factors (e.g., 10,000 at 10 GHz). The dimensions of a dielectric resonator and its environment determine resonant frequency which generally ranges from 1 GHz to 100 GHz.
Conventional dielectric resonator oscillators, however, have an inherent delay time after being turned on before a full power oscillation is generated. As is well known in the art, an oscillator employs positive feedback to continuously recirculate an amplified signal through the resonant circuit to build up oscillations. In general, the amplified signal must recirculate many times after the oscillator's active device is turned on before a pulse begins to rise. For this reason, the resonant circuit introduces a delay of several microseconds and, thus, limits the oscillator's performance.
Generally, Q is 2.pi. times the ratio of maximum stored energy to the energy dissipated per cycle at a given frequency. Thus, the time delay through a resonant circuit is directly proportional to its loaded Q factor (the loaded Q of a system is the value of Q obtained when the system is coupled to a device that dissipates energy). For this reason, an oscillator having a lower Q factor provides a faster turn-on time. However, conventional oscillators having lower Q factors for providing faster turn-on times are more sensitive to temperature variations and perform inadequately over a broad range of temperatures.